In replacing the knee joint which has been damaged due to disease or trauma, it is important that the damaged bone at the proximal end of the tibia be removed by cutting it at an appropriate varus/valgus angle and at an appropriate flexion/extension angle. In this manner, the bone cut will be in the correct varus/valgus and flexion/extension alignment, and the proximal end of the tibia can then receive an implant or prosthesis to reconstruct a functioning knee joint. Proper fit and function of the implant will depend on the accuracy of the cut.
Many devices for determining the correct angle of the bone cut are known in the art. The known devices typically include a cutting block which guides a saw blade and an anterior telescoping rod or similar device which extends to a position adjacent the approximate center of the anterior face of the patient's ankle or talus to allow the surgeon to duplicate the mechanical axis of the tibia as a reference guide for the proper alignment of the cutting block with the mechanical axis.
Johnson et al., U.S. Pat. No. 5,451,228 (Johnson) discloses a tibial resector guide having an angularly adjustable head controlled by a thumb actuated slide mechanism. The tibial resector guide disclosed by Johnson includes only one telescoping rod to reference the mechanical axis, but no external side rod or similar means to reference the mid-coronal plane.
Ferrante et al., U.S. Pat. No. 5,342,367 (Ferrante) discloses a tibial cutting guide which does not include any means for external referencing, such as extending rods.
Bowman et al., U.S. Pat. No. 4,952,213 (Bowman) discloses using an intramedullary rod connected to a pivot device carrying the bone saw guide. There is no external referencing rod disclosed in Bowman--rather, the reference used is the intramedullary rod inserted deep into the bone canal.
Petersen, U.S. Pat. No. 5,342,368 (Petersen) discloses a proximal tibial resector guide including an intramedullary rod which is attached at its proximal end to a bar provided for the cutting saw guide. There is no external referencing rod disclosed in Peterson--rather, the reference used is the intramedullary rod inserted deep into the bone canal.
Petersen, U.S. Pat. No. 4,524,766 (Petersen) discloses a surgical knee alignment system including a tibial resection saw guide which is mounted on one telescoping external rod used to reference the mechanical axis. There is no external side rod or similar means disclosed to reference the mid-coronal plane.
Wehrli, U.S. Pat. No. 4,938,762 (Wehrli) discloses a reference system for the implantation of condylar total knee prostheses, including a tibial resection saw guide. The Wehrli system utilizes as a main reference point a screw placed in the pelvis, and includes a number of screws placed into the tibia. Telescoping rods attached to the pelvic bone screw and the tibial bone screw are utilized to position the tibial resection saw guide.
One drawback of the use of intramedullary rods as references is that the anatomy of many patients does not permit an intramedullary rod to be fully inserted. Also, the prior art which utilizes only one external referencing rod adjacent the anterior portion of the bone does not provide a direct and reliable means of referencing the mid-coronal plane. The present invention provides external rods for directly and reliably referencing both the mechanical axis and the mid-coronal plane.
Citation or identification of any reference in Section 2 or any section of this application should not be construed as an admission that such reference is available as prior art to the present invention.